Conventionally, power conversion apparatuses including a matrix converter have been in practical use (see Patent Literature (PTL) 1 and PTL 2, for example).
FIG. 24 is a circuit diagram of a matrix converter 200 disclosed in PTL 1. To drive a three-phase motor 203 using a single-phase AC power supply 201, the matrix converter 200 directly converts an input AC voltage supplied from the single-phase AC power supply 201 into a three-phase output AC voltage using bidirectional switches 202a to 202f, and supplies the output AC voltage of each phase to a winding of a corresponding phase of the three-phase motor 203.
Each of the bidirectional switches 202a to 202f includes two switching elements connected in inverse parallel, each capable of changing between a unidirectional conducting state and a non-conducting state. A magnitude determining unit 204 determines the magnitude relationship between the voltages at the terminals of the single-phase AC power supply 201. According to the magnitude relationship determined by the magnitude determining unit 204, a control unit 205 supplies a current to the windings of the three-phase motor 203 from the single-phase AC power supply 201, and controls the conduction of each of the bidirectional switches 202a to 202f to allow circulation of a regenerative current from the windings of the three-phase motor 203.
According to PTL 1, the matrix converter 200 having the above configuration allows the motor driving current to be stable, highly efficient, and highly reliable without a short circuit.
PTL 2 discloses a similar technique for driving a three-phase motor with a single-phase AC power supply, using a matrix converter.
For home appliances, a two-phase motor is often used as it is simple in configuration and favorable for miniaturization compared to the three-phase motor. Most of the two-phase motors that operate from a household single-phase AC power supply are capacitor motors which generate a rotating magnetic field for a start-up, by applying a two-phase AC voltage generated from the single-phase AC power supply using a capacitor to a main winding and an auxiliary winding (see PTL 3, for example).
FIG. 25 is a circuit diagram of a capacitor motor 300 disclosed in PTL 3, illustrating a typical example of connection of windings 302 and 303, a capacitor 304, and an AC power supply 301. PTL 3 discloses a technique of switching among a plurality of rotation speeds of the capacitor motor by simply changing the connection of the capacitor, the windings, and the AC power supply, without a need to add a center tap for the windings or an external reactor.